Calcium
Major mineralsYour intake
What each level of calcium does
Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.
- Severely lowYOU ARE HERE0 mg – 429 mg
Well below target. Risk of deficiency symptoms tied to bone · muscle.
- Insufficient429 mg – 1300 mg
Below the recommended daily target. Long-term adequacy not assured.
- Adequate1300 mg – 1950 mg
Daily target met. Standard nutritional support for bone · muscle.
- Therapeutic1950 mg – 2496 mg
Common for specific health goals. Check the evidence for your situation before sustaining this level.
- Over upper limit2500 mg – +
Above the tolerable upper limit. Risk of adverse effects — back off or consult a clinician.
Overview
Most abundant mineral in the human body — 99% stored in bones and teeth as hydroxyapatite. The remaining 1% in blood and soft tissue is tightly regulated (parathyroid hormone, calcitonin, calcitriol) because of its central role in muscle contraction, nerve signalling, and coagulation.
Functions
- ●Structural component of bone and teeth (hydroxyapatite)
- ●Triggers skeletal and cardiac muscle contraction
- ●Required for synaptic neurotransmitter release
- ●Cofactor in coagulation cascade (factor IV)
- ●Secondary messenger in numerous intracellular signalling cascades
Mechanism
Bone serves as the calcium bank. When serum calcium drops, parathyroid hormone (PTH) increases bone resorption, renal reabsorption, and (via calcitriol) gut absorption. Chronic dietary insufficiency forces ongoing bone withdrawal, driving osteopenia and osteoporosis over decades. Adequate vitamin D and a sufficient bone-calcium reservoir established by young adulthood are the levers that matter.
Benefits
- ●Reduces fracture risk in older adults when combined with vitamin D
- ●Supports peak bone mass accrual in children and adolescents
- ●Modestly reduces premenstrual symptoms (~1,200 mg/day)
- ●May reduce risk of colorectal adenomas (modest, mixed evidence)
Deficiency
Frank hypocalcemia is uncommon (homeostasis maintains serum) but inadequate intake drives long-term bone loss without acute symptoms. ~40% of US adults fail to meet RDA.
- ●Osteopenia, osteoporosis, fragility fractures (long-term)
- ●Muscle cramps, tetany (acute hypocalcemia)
- ●Numbness, tingling around mouth
- ●Brittle nails, dental issues
- ●Postmenopausal women (estrogen loss accelerates resorption)
- ●Vegans without fortified plant milks
- ●Lactose-intolerant adults
- ●Long-term PPI users
- ●Chronic glucocorticoid therapy
Excess
Excess from supplements (not food) may increase cardiovascular event risk and kidney stones. Food calcium does not show this association.
- ●Kidney stones
- ●Hypercalcemia — fatigue, constipation, confusion
- ●Vascular calcification (high-dose supplement, low-K2 context)
- ●Milk-alkali syndrome (historical)
Forms
- Calcium carbonate40% elemental Ca; cheapest; needs stomach acid (take with food)
- Calcium citrate21% elemental; absorbs without acid; preferred for older adults on PPIs
- Calcium malate, gluconate, lactateLower elemental %; better tolerance, higher pill burden
- Calcium hydroxyapatite (MCHA)Bovine bone derivative; emerging bone-density data
Food sources
- Plain yogurt · 1 cup450 mg
- Milk · 1 cup300 mg
- Tofu (calcium-set) · 1/2 cup430 mg
- Canned sardines (with bones) · 3 oz325 mg
- Cooked collard greens · 1 cup270 mg
- Fortified plant milk · 1 cup300 mg
Supplement forms
Calcium citrate absorbs equally well with or without food and is preferred for older adults on PPIs. Calcium carbonate is cheaper but needs stomach acid to absorb — take with meals. Avoid single doses above 500 mg of elemental calcium; absorption efficiency drops sharply. Pair with vitamin D for full benefit.
Bioavailability
Active absorption is vitamin-D-dependent (duodenum); passive paracellular absorption (jejunum/ileum) dominates above ~10% saturation. Absorption efficiency drops with dose — 500 mg cap per sitting is the practical ceiling. Phytate (whole grains), oxalate (spinach, rhubarb), and high-dose iron all reduce uptake. Bioavailability from low-oxalate greens (kale, bok choy) is actually higher than from milk.
Longevity relevance
Adequacy through midlife builds the bone reserve drawn down by aging. Post-menopause, calcium + D + resistance exercise + K2 cooperate to slow loss. Pure calcium-mega-dose supplementation without other co-factors may shift cardiovascular risk — total intake (food + supplement) should aim at RDA, not greatly exceed it.
Relationships
- Vitamin D · Required for active intestinal absorption
- Vitamin K2 · Activates osteocalcin to direct calcium into bone matrix
- Magnesium · Required for PTH secretion and vitamin D activation
- Protein · Higher protein intake improves calcium retention in older adults (modern view; old 'protein leaches calcium' claim is outdated)
- Oxalate (spinach, rhubarb, almonds) · Forms insoluble calcium oxalate; reduces absorption from those foods
- Phytate (whole grains, legumes) · Binds calcium; meaningful in high-phytate diets
- Iron supplements (high dose) · Compete for absorption; separate by 2 hours
- Caffeine, sodium (high) · Increase urinary calcium loss; modest effect
References
About Calcium
Bone mineralization, muscle contraction, neuronal signaling.
- Role
- Bone · muscle
- Daily target
- 1300 mg (DV)
- Upper limit
- 2500 mg
- Also called
- calcium, calcium carbonate, calcium citrate, calcium malate, calcium hydroxyapatite
Forms with lower absorption: carbonate. Prefer better-absorbed forms when supplementing.
The mechanisms and systems this nutrient feeds. Click any to drill into what runs on it.
Top food sources of Calcium
Whole foods that contribute meaningfully (≥10% DV per 100 g serving). Click any food to see its full nutrient profile and what else it brings to the table.